PRACTICAL FIXATIVE SOLUTIONS 61 



The only notable defect of Zenker is a tendency to crumple 

 collagen fibres. 



flemming's strong fluid (1884)" 



Distilled water . . . . . 0-8 ml 



Chromium trioxide, 5 ^o aq. . . 0-3 ml 



Osmium tetroxide, 2% aq. . . 0-4 ml 



Acetic acid, 20% (or less) aq. . . 0-5 ml 



As a general rule, use the full concentration of acetic acid. 



pH 1-4;^^ the amount of acetic acid used does not affect the pH.^*^ 



Use pieces 2 mm or less in thickness. 



Wash out for several hours in running water or repeated changes. 



Since 2 ml of the mixture are sufficient for the fixation of the 

 small pieces of tissue that should be used, it is desirable to follow 

 the formula given above. There is then no wastage of the ex- 

 tremely expensive osmium tetroxide. The fluid made up in this 

 way has the same composition as that which results from the use 

 of Flemming's own formula. 



Flemming contains a trio of ingredients that are found over and 

 over again in successful mixtures ; namely, 



(1) one or more coagulants of protein (in this case chromium 

 trioxide) ; 



(2) a non-coagulant fixative of protein (in this case osmium 

 tetroxide) ; 



(3) acetic acid. 



One might suppose that the best results would be given by non- 

 coagulant fixatives in the absence of coagulants; but tissue that 

 has been treated with no other fixative of protein than a non- 

 coagulant does not give ready access to paraffin, and the prepara- 

 tion of good paraffin sections is often difficult. This particularly 

 applies to osmium tetroxide. The spongework produced by coagu- 

 lants provides spaces into which melted paraffin can enter (p. 75). 

 Beyond this, coagulants give the best fixation of chromosomes, 

 and chromium trioxide is pre-eminent in this respect. If, how- 

 ever, no non-coagulant fixative of proteins is included, the sponge- 

 work tends to be unduly coarse, and c)1;oplasmic inclusions are 



